Airdrie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Airdrie clear sky chart from 2005-11-06 to 2025-05-11.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	8% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	117300
	Night	6% 9% 4 9% 6% 5% 5% 4 6% 8% 36%	120371
Transparency	Day	43% 5% 15% 24% 11% 2	117046
	Night	44% 5% 15% 23% 12% 2	120271
Seeing	Day	14% 10% 29% 29% 14% 4	15930
	Night	11% 8% 33% 33% 13% 2	25175

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	2 8% 6% 14% 8% 8% 6% 4 6% 7% 32%	3179
	11th to 20th	Day	2 8% 4 11% 6% 6% 6% 5% 8% 8% 37%	3220
	21st to end	Day	3 6% 3 8% 5% 5% 5% 4 6% 10% 44%	4004
February	1st to 10th	Day	3 12% 5% 12% 7% 6% 7% 4 7% 8% 28%	1600
	11th to 20th	Day	6% 9% 4 11% 8% 6% 8% 5% 8% 8% 28%	1737
	21st to end	Day	4 11% 5% 11% 6% 6% 6% 5% 7% 9% 31%	1605
March	1st to 10th	Day	2 9% 4 12% 6% 5% 6% 4 6% 10% 36%	4518
	11th to 20th	Day	4 11% 5% 9% 4 4 5% 4 6% 8% 39%	4945
	21st to end	Day	8% 22% 7% 13% 6% 5% 5% 4 5% 6% 19%	5571
April	1st to 10th	Day	7% 17% 5% 11% 5% 5% 5% 4 6% 8% 27%	2455
	11th to 20th	Day	10% 15% 5% 9% 6% 5% 4 5% 6% 7% 28%	2570
	21st to end	Day	11% 13% 4 8% 6% 5% 4 4 6% 8% 30%	2600
May	1st to 10th	Day	16% 15% 4 8% 5% 5% 5% 4 5% 6% 29%	4505
	11th to 20th	Day	11% 9% 4 9% 6% 6% 6% 5% 7% 9% 29%	4697
	21st to end	Day	17% 10% 3 10% 7% 7% 6% 5% 6% 6% 23%	5161
June	1st to 10th	Day	17% 7% 3 8% 6% 5% 6% 5% 8% 8% 27%	2850
	11th to 20th	Day	19% 10% 3 9% 5% 5% 6% 5% 7% 7% 24%	2850
	21st to end	Day	8% 5% 2 7% 6% 6% 6% 4 7% 9% 39%	2850
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 9% 45%	4740
	11th to 20th	Day	8% 3 2 4 3 4 5% 5% 8% 11% 48%	4740
	21st to end	Day	4 3 2 5% 4 4 5% 4 6% 10% 54%	5027
August	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 5% 7% 9% 42%	4401
	11th to 20th	Day	7% 5% 2 5% 5% 4 5% 5% 8% 11% 43%	4086
	21st to end	Day	9% 4 1 5% 3 4 4 3 6% 8% 51%	4521
September	1st to 10th	Day	10% 6% 3 6% 4 4 4 3 5% 8% 48%	2359
	11th to 20th	Day	15% 8% 2 5% 4 3 5% 3 6% 7% 42%	2090
	21st to end	Day	9% 8% 3 7% 4 4 4 4 6% 8% 43%	2090
October	1st to 10th	Day	7% 7% 3 8% 4 5% 5% 4 7% 10% 41%	3344
	11th to 20th	Day	5% 7% 2 7% 4 5% 6% 5% 8% 10% 41%	2908
	21st to end	Day	7% 7% 3 7% 6% 5% 5% 5% 5% 6% 44%	3101
November	1st to 10th	Day	7% 16% 5% 9% 5% 5% 5% 4 5% 8% 30%	1632
	11th to 20th	Day	5% 13% 3 8% 6% 5% 5% 4 7% 7% 37%	1514
	21st to end	Day	4 13% 4 9% 5% 5% 4 4 7% 10% 34%	1400
December	1st to 10th	Day	3 11% 5% 13% 6% 7% 5% 5% 6% 7% 32%	2290
	11th to 20th	Day	3 10% 4 10% 7% 8% 8% 5% 7% 7% 30%	2642
	21st to end	Day	2 10% 4 9% 5% 5% 6% 4 6% 7% 42%	3498
January	1st to 10th	Night	3 12% 5% 14% 9% 8% 7% 4 6% 7% 25%	6766
	11th to 20th	Night	2 7% 4 13% 6% 6% 6% 6% 7% 7% 34%	6721
	21st to end	Night	2 9% 4 9% 5% 5% 5% 4 6% 8% 41%	6952
February	1st to 10th	Night	4 10% 5% 11% 8% 8% 6% 5% 6% 8% 30%	2800
	11th to 20th	Night	4 11% 6% 11% 7% 6% 6% 5% 8% 8% 29%	2548
	21st to end	Night	2 11% 5% 11% 8% 5% 6% 4 6% 8% 33%	2025
March	1st to 10th	Night	3 8% 4 13% 7% 6% 6% 5% 6% 10% 34%	5376
	11th to 20th	Night	5% 8% 4 10% 5% 6% 6% 5% 7% 9% 37%	5054
	21st to end	Night	8% 19% 6% 15% 7% 5% 4 4 6% 7% 21%	5402
April	1st to 10th	Night	8% 13% 3 11% 6% 5% 5% 5% 7% 8% 29%	1944
	11th to 20th	Night	10% 12% 6% 11% 6% 5% 5% 5% 5% 6% 29%	1781
	21st to end	Night	11% 11% 5% 9% 6% 5% 5% 5% 6% 8% 31%	1800
May	1st to 10th	Night	15% 15% 4 8% 5% 5% 4 4 5% 6% 30%	2677
	11th to 20th	Night	9% 7% 3 7% 6% 5% 6% 5% 8% 10% 34%	2202
	21st to end	Night	14% 10% 3 10% 7% 6% 7% 6% 7% 7% 24%	2414
June	1st to 10th	Night	16% 8% 3 8% 6% 4 5% 5% 6% 6% 33%	1330
	11th to 20th	Night	18% 8% 4 6% 6% 5% 6% 5% 6% 7% 29%	1330
	21st to end	Night	8% 5% 3 6% 5% 6% 6% 4 8% 9% 41%	1330
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 4 7% 8% 46%	2220
	11th to 20th	Night	6% 3 2 5% 4 5% 5% 5% 10% 10% 46%	2220
	21st to end	Night	4 4 1 5% 4 4 4 4 5% 8% 55%	2521
August	1st to 10th	Night	9% 6% 2 7% 4 4 5% 4 7% 9% 43%	2529
	11th to 20th	Night	7% 4 2 7% 5% 4 6% 4 8% 12% 43%	2751
	21st to end	Night	8% 4 1 6% 4 3 3 3 6% 9% 52%	3146
September	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 6% 8% 48%	1816
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 5% 8% 46%	2090
	21st to end	Night	10% 7% 2 5% 4 4 4 4 7% 8% 45%	2090
October	1st to 10th	Night	8% 7% 2 6% 4 4 4 4 6% 8% 48%	3631
	11th to 20th	Night	6% 8% 2 6% 4 5% 5% 4 6% 7% 47%	4019
	21st to end	Night	5% 7% 3 7% 5% 5% 5% 5% 7% 7% 43%	4457
November	1st to 10th	Night	7% 13% 5% 8% 5% 4 5% 4 6% 7% 35%	2646
	11th to 20th	Night	3 11% 4 8% 6% 5% 6% 5% 6% 8% 37%	2885
	21st to end	Night	4 11% 4 9% 6% 6% 5% 4 7% 9% 35%	3000
December	1st to 10th	Night	4 11% 4 11% 6% 7% 6% 5% 7% 9% 32%	4890
	11th to 20th	Night	4 11% 5% 13% 8% 7% 5% 4 6% 8% 29%	5550
	21st to end	Night	3 10% 4 9% 5% 5% 5% 5% 6% 7% 40%	7458

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	51% 4 10% 22% 11% 2	3179
	11th to 20th	Day	43% 5% 13% 16% 20% 3	3241
	21st to end	Day	35% 5% 15% 31% 14% 1	4004
February	1st to 10th	Day	52% 6% 14% 17% 10% 2	1600
	11th to 20th	Day	51% 5% 12% 22% 9% 2	1746
	21st to end	Day	48% 5% 12% 20% 12% 2	1605
March	1st to 10th	Day	41% 6% 14% 21% 16% 1	4518
	11th to 20th	Day	41% 5% 14% 24% 15% 1	4946
	21st to end	Day	64% 6% 12% 12% 6% 1	5571
April	1st to 10th	Day	54% 6% 14% 18% 8% 1	2455
	11th to 20th	Day	53% 6% 11% 20% 9% 1	2570
	21st to end	Day	52% 5% 14% 21% 9% 1	2600
May	1st to 10th	Day	56% 3 12% 23% 6% 1	4505
	11th to 20th	Day	46% 7% 14% 23% 9%	4701
	21st to end	Day	58% 5% 14% 15% 6% 1	5162
June	1st to 10th	Day	51% 6% 15% 18% 8% 1	2850
	11th to 20th	Day	56% 6% 15% 16% 7% 2	2850
	21st to end	Day	38% 7% 20% 25% 9% 2	2850
July	1st to 10th	Day	32% 6% 16% 26% 16% 4	4666
	11th to 20th	Day	28% 6% 20% 34% 10% 1	4659
	21st to end	Day	25% 5% 14% 29% 22% 5%	4868
August	1st to 10th	Day	36% 5% 18% 34% 6% 1	4384
	11th to 20th	Day	32% 6% 26% 28% 6% 1	4126
	21st to end	Day	31% 4 21% 33% 11% 1	4520
September	1st to 10th	Day	35% 4 17% 26% 14% 5%	2359
	11th to 20th	Day	41% 4 15% 26% 12% 2	2090
	21st to end	Day	39% 5% 14% 27% 12% 3	2090
October	1st to 10th	Day	37% 5% 19% 32% 6% 1	3344
	11th to 20th	Day	36% 5% 21% 24% 12% 2	2908
	21st to end	Day	39% 5% 11% 33% 12% 1	3101
November	1st to 10th	Day	51% 6% 10% 20% 10% 2	1632
	11th to 20th	Day	44% 4 16% 23% 10% 2	1514
	21st to end	Day	45% 5% 17% 23% 10% 2	1400
December	1st to 10th	Day	50% 5% 13% 22% 7% 2	2290
	11th to 20th	Day	50% 4 19% 19% 7% 1	2644
	21st to end	Day	39% 5% 11% 23% 18% 4	3498
January	1st to 10th	Night	56% 5% 11% 20% 6% 2	6766
	11th to 20th	Night	47% 4 13% 18% 14% 4	6762
	21st to end	Night	40% 4 15% 26% 14% 1	6952
February	1st to 10th	Night	51% 5% 11% 19% 12% 3	2800
	11th to 20th	Night	49% 5% 13% 20% 11% 2	2549
	21st to end	Night	46% 5% 11% 23% 14% 2	2025
March	1st to 10th	Night	43% 6% 17% 20% 12% 2	5376
	11th to 20th	Night	41% 7% 14% 23% 14% 1	5054
	21st to end	Night	62% 5% 11% 13% 8% 1	5402
April	1st to 10th	Night	49% 6% 12% 20% 11% 1	1944
	11th to 20th	Night	53% 4 11% 21% 10% 1	1781
	21st to end	Night	49% 5% 14% 22% 9% 2	1800
May	1st to 10th	Night	54% 5% 11% 21% 8% 1	2677
	11th to 20th	Night	40% 6% 15% 29% 10% 1	2202
	21st to end	Night	55% 7% 15% 16% 6% 1	2414
June	1st to 10th	Night	49% 5% 16% 19% 10% 1	1330
	11th to 20th	Night	51% 6% 15% 17% 7% 3	1330
	21st to end	Night	37% 6% 23% 25% 8% 1	1330
July	1st to 10th	Night	33% 6% 16% 24% 18% 3	2185
	11th to 20th	Night	28% 6% 22% 31% 9% 4	2178
	21st to end	Night	26% 6% 12% 32% 20% 4	2441
August	1st to 10th	Night	35% 5% 16% 33% 11% 1	2521
	11th to 20th	Night	33% 6% 26% 27% 8% 1	2777
	21st to end	Night	28% 5% 22% 33% 11% 2	3146
September	1st to 10th	Night	35% 4 15% 26% 15% 5%	1816
	11th to 20th	Night	38% 4 16% 26% 12% 4	2090
	21st to end	Night	35% 5% 18% 25% 14% 4	2090
October	1st to 10th	Night	33% 5% 17% 26% 17% 1	3631
	11th to 20th	Night	35% 4 18% 27% 14% 2	4019
	21st to end	Night	38% 5% 11% 32% 13% 1	4457
November	1st to 10th	Night	47% 5% 13% 22% 11% 2	2646
	11th to 20th	Night	43% 5% 16% 21% 14% 1	2885
	21st to end	Night	44% 6% 16% 21% 10% 3	3000
December	1st to 10th	Night	48% 6% 16% 21% 7% 2	4890
	11th to 20th	Night	52% 4 17% 18% 8% 1	5547
	21st to end	Night	40% 4 10% 24% 16% 4	7458

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 12% 35% 27% 13% 8%	200
	11th to 20th	Day	9% 11% 41% 25% 13% 2	200
	21st to end	Day	10% 10% 37% 30% 11% 3	220
February	1st to 10th	Day	13% 16% 34% 22% 11% 5%	200
	11th to 20th	Day	7% 11% 40% 29% 10% 2	292
	21st to end	Day	9% 13% 33% 31% 13% 2	369
March	1st to 10th	Day	9% 16% 34% 28% 11% 3	500
	11th to 20th	Day	10% 13% 36% 28% 11% 3	500
	21st to end	Day	17% 15% 34% 21% 9% 4	550
April	1st to 10th	Day	16% 16% 34% 23% 9% 2	500
	11th to 20th	Day	16% 14% 31% 27% 10% 2	492
	21st to end	Day	20% 14% 25% 27% 11% 2	500
May	1st to 10th	Day	21% 11% 25% 26% 14% 3	553
	11th to 20th	Day	18% 8% 24% 30% 16% 5%	676
	21st to end	Day	19% 9% 20% 29% 19% 4	734
June	1st to 10th	Day	18% 9% 29% 29% 12% 3	680
	11th to 20th	Day	23% 10% 25% 27% 13% 3	680
	21st to end	Day	11% 6% 27% 32% 19% 5%	680
July	1st to 10th	Day	12% 5% 23% 36% 20% 4	671
	11th to 20th	Day	13% 5% 26% 31% 22% 3	668
	21st to end	Day	5% 6% 27% 36% 19% 6%	677
August	1st to 10th	Day	14% 6% 24% 32% 19% 5%	487
	11th to 20th	Day	10% 4 26% 36% 20% 5%	477
	21st to end	Day	11% 9% 23% 31% 19% 7%	539
September	1st to 10th	Day	13% 9% 30% 28% 14% 6%	490
	11th to 20th	Day	20% 7% 25% 29% 15% 5%	490
	21st to end	Day	14% 15% 31% 28% 9% 3	490
October	1st to 10th	Day	17% 8% 31% 27% 14% 4	409
	11th to 20th	Day	11% 13% 35% 27% 11% 3	300
	21st to end	Day	15% 14% 36% 24% 9% 2	330
November	1st to 10th	Day	15% 12% 34% 29% 8% 2	300
	11th to 20th	Day	16% 13% 40% 23% 7% 2	256
	21st to end	Day	8% 12% 38% 26% 11% 6%	200
December	1st to 10th	Day	8% 12% 40% 28% 11% 3	200
	11th to 20th	Day	9% 12% 43% 22% 12% 3	200
	21st to end	Day	7% 9% 34% 30% 18% 3	220
January	1st to 10th	Night	8% 12% 37% 30% 11% 1	1000
	11th to 20th	Night	8% 10% 43% 30% 8% 1	995
	21st to end	Night	11% 15% 38% 28% 8% 1	880
February	1st to 10th	Night	9% 12% 32% 33% 12% 3	800
	11th to 20th	Night	9% 8% 36% 34% 11% 2	784
	21st to end	Night	7% 10% 34% 29% 17% 4	660
March	1st to 10th	Night	8% 8% 36% 34% 12% 3	800
	11th to 20th	Night	9% 7% 36% 35% 12% 2	800
	21st to end	Night	12% 7% 30% 36% 12% 3	880
April	1st to 10th	Night	13% 8% 31% 31% 16% 1	744
	11th to 20th	Night	16% 7% 35% 33% 9%	593
	21st to end	Night	16% 8% 30% 35% 10%	600
May	1st to 10th	Night	17% 11% 26% 31% 14% 1	494
	11th to 20th	Night	13% 7% 29% 37% 13% 1	375
	21st to end	Night	22% 5% 22% 33% 17%	411
June	1st to 10th	Night	21% 6% 29% 29% 14% 1	380
	11th to 20th	Night	21% 4 28% 33% 12% 1	380
	21st to end	Night	11% 3 22% 46% 17% 1	380
July	1st to 10th	Night	10% 4 18% 41% 26% 1	370
	11th to 20th	Night	13% 3 23% 39% 20% 2	368
	21st to end	Night	5% 5% 20% 44% 24% 2	416
August	1st to 10th	Night	12% 3 13% 42% 28% 2	378
	11th to 20th	Night	9% 2 20% 44% 22% 2	528
	21st to end	Night	11% 4 22% 41% 22% 1	627
September	1st to 10th	Night	14% 4 23% 38% 18% 2	665
	11th to 20th	Night	16% 5% 21% 38% 18% 2	760
	21st to end	Night	13% 6% 31% 33% 14% 2	760
October	1st to 10th	Night	14% 7% 29% 33% 15% 2	760
	11th to 20th	Night	12% 6% 34% 33% 13% 2	760
	21st to end	Night	12% 9% 33% 36% 9% 1	836
November	1st to 10th	Night	14% 11% 37% 28% 9% 1	891
	11th to 20th	Night	9% 12% 46% 25% 7% 1	1000
	21st to end	Night	9% 11% 41% 31% 8% 2	1000
December	1st to 10th	Night	10% 11% 38% 28% 11% 2	1000
	11th to 20th	Night	7% 10% 41% 34% 8% 1	1000
	21st to end	Night	8% 10% 38% 32% 9% 2	1100

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